1. Field of the Invention
The present invention relates to a miniature electric motor for generating vibration used as a vibration generator, such as a mobile phone.
2. Description of the Related Art
In some current portable type telecommunication devices, such as mobile phones (cellular phone), a mechanism for paging a specific person by utilizing vibration in order not to cause troubles to other persons in the neighborhood of him or her instead of generating paging sound has been extensively used.
A miniature electric motor for generating vibration is provided in such a portable type telecommunication device. In such a motor, a rotary shaft is inserted into a hole of a vibrator so that the vibrator is mounted on the motor.
While the motor rotates, the rotary shaft vibrates due to imbalance of the center of gravity of the vibrator. Then, the motor as a whole vibrates to thereby vibrate the portable type telecommunication device.
The rotary shaft of the motor has a circular shape in cross-section and has to stand against the vibration. Accordingly, there have conventionally been proposed various approaches for technical means for fixing the vibrator to the rotary shaft. In many cases, the vibrator is crimped and plastically deformed so that the vibrator may be fixed to the rotary shaft. As another technical approach, the rotary shaft is press-fitted in a hole, having a circular shape in cross-section, of a vibrator.
As still another technique, an annular recess portion is formed around an overall circumferential area of the rotary shaft. Then, a crimped portion of the vibrator is gripped in the recess portion and is plastically deformed to enter through the outer circumferential surface of the rotary shaft. Thus, the retaining strength of the vibrator to the rotary shaft may be obtained.
In these related art, assuming that the rotary shaft has a circular shape in cross-section, a variety of approaches have been taken on the vibrator side to fix the vibrator to the rotary shaft. However, in any approach, it is difficult to positively fix the vibrator to the rotary shaft with a large force under the condition in which the vibrator is not rotated relative to the rotary shaft having the circular shape in cross-section. For this reason, there is a limit to the improvement in retaining force of the vibrator to the rotary shaft.
Also, in the case in which the rotary shaft is press-fitted and fixed in the hole of the vibrator, a large pressure is needed. As a result, there is a fear that a load would be applied to a motor body to cause adverse affects.
As another technique for an approach to the rotary shaft per se, in addition to the case in which the recess portion is formed around the entire circumference of the rotary shaft as described above, there is a case in which knurled mesh is applied to the surface of the rotary shaft through a knurling method to thereby perform the mat finishing.
If this mat finishing is performed, the retaining force of the vibrator to the rotary shaft is rather enhanced but there is a demand for the technique to further enhance the retaining force. Also, in order to perform the above-described mat finishing, it is necessary to spend time, work and high cost with rather complicated steps.
By the way, in case of the miniature electric motor for generating vibration, one force in a thrust direction (in the center axis direction) and the other force in a rotational direction are applied between the rotary shaft and the vibrator. The force in the rotational direction is a force to rotate the rotary shaft relative to the vibrator round the center axis. The force in the thrust direction is a force to move the vibrator relative to the rotary shaft in the center axis direction. In this motor, since the vibrator having a large mass relative to the motor is rotated, the force in the rotational direction is much larger than the force in the thrust direction.
However, in each conventional technique described above, since the rotary shaft has a circular shape in cross-section, it is difficult to fix the vibrator to the rotary shaft with a large force under a relatively non-rotatable condition of the vibrator against the force of the rotational force.
In order to overcome the above-noted defects, an object of the present invention is to provide a miniature electric motor for generating vibration in which a vibrator may be positively fixed to a rotary shaft with a large retaining force under a relatively non-rotatable condition so as not to be moved in the thrust direction.
In order to attain this and other objects, according to the present invention, there is provided a miniature electric motor for generating vibration on which a vibrator is mounted on an output portion of a rotary shaft rotatably supported to a casing, wherein the output portion of the rotary shaft is formed into an irregular shape in cross-section other than a circular shape in cross-section, an engaging hole having a predetermined shape in cross-section, which corresponds to the irregular shape in cross-section of the output portion and which makes the vibrator to be kept under a relatively non-rotatable condition to the rotary shaft, is formed in the vibrator, and the output portion is engaged with the engaging hole and the vibrator is positioned and held in a thrust direction relative to the output portion to thereby fix the vibrator to the rotary shaft.
In the miniature motor for generating vibration in accordance with a preferred specific embodiment, the output portion of the rotary shaft is depressed from at least one side to form at least one flat surface portion in a longitudinal direction of the output portion, the engaging hole having the predetermined shape in cross-section corresponding to the irregular shape in cross-section of the output portion is formed in the vibrator, and the output portion is fitted in the engaging hole so that the vibrator is kept under the non-rotatable condition relative to the rotary shaft, and wherein a tip end portion of the output portion projecting from the engaging hole to the outside is depressed so that a part of the tip end portion is plastically deformed radially outwardly, and the vibrator is positioned and held in the thrust direction to the output portion by the tip end portion and a stepped portion formed at an end portion of the flat surface portion toward the casing, whereby the vibrator is fixed to the rotary shaft.
Preferably, both sides of the output portion are depressed so that the output portion is plastically deformed and a couple of flat surface portions are simultaneously formed in parallel with each other in a longitudinal direction of the output portion.
Incidentally, a couple of flat surface portions may be formed in parallel with each other on the output portion by machining.
Preferably, an end face of an tip end portion of the output portion is substantially flush with or somewhat retracted from a flat end face of the vibrator located away from the casing, and the end face is not projecting at least from the flat end face to the outside.
Preferably, under the condition in which the output portion is fitted in the engaging hole for a clearance fitting, a projecting portion of the vibrator in which the engaging hole is formed is depressed and plastically deformed, whereby an outer surface of the output portion and an inner surface of the engaging hole of the projecting portion are brought into intimate contact with each other.
Also, it is preferable that the output portion is press-fitted into the engaging hole under such a small pressure in which the vibrator does not fall apart.
It is preferable that the projecting portion provided to a body portion of the vibrator and provided with the engaging hole has a predetermined dimension in a center axis direction which is shorter than a full length of the vibrator in the center axis direction and the projecting portion is disposed in a position in the vicinity of the casing.
In another embodiment of the present invention, the projecting portion provided in a body portion of the vibrator and provided with the engaging hole has a predetermined dimension in a center axis direction which is shorter than a full length of the vibrator in the center axis direction and the projecting portion is disposed in a substantially central portion in the center axis direction of the body portion.
In one embodiment, the vibrator has symmetrical shape in the center axis direction, and if the vibrator is turned through 180 degrees and then is mounted on the rotary shaft, the same posture is obtained, therefore there is no orientation when the vibrator is to be mounted.
It is preferable that a projecting portion of the vibrator in which the engaging hole is formed is positioned and held in the thrust direction under the condition in which the projecting portion is supported between the stepped portion and the tip end portion of the output portion.
In another embodiment of the present invention, the engaging hole having a rectangular shape in cross-section is formed in the vibrator, one flat surface portion is formed in the output portion, and the flat surface portion is brought into contact with one inner surface of the engaging hole, and while the output portion is engaged with the engaging hole, the flat surface portion and the inner surface are brought into contact with each other whereby the vibrator is fixed to the rotary shaft under the relatively non-rotatable condition.
In still another embodiment of the present invention, the output portion has an ellipse shape in cross-section and the engaging hole has a rectangular shape in cross-section whereby the vibrator is fixed to the rotary shaft under the relatively non-rotatable condition.
Incidentally, wherein the output portion may have an oval figure in cross-section and the engaging hole has a rectangular shape in cross-section whereby the vibrator is fixed to the rotary shaft under the relatively non-rotatable condition. The output portion and the engaging hole may have a triangle shape in cross-section together whereby the vibrator is fixed to the rotary shaft under the relatively non-rotatable condition. The output portion and the engaging hole may have a rectangular shape in cross-section together whereby the vibrator is fixed to the rotary shaft under the relatively non-rotatable condition. The output portion may have a hexagonal shape in cross-section and the engaging hole has a rectangular shape in cross-section whereby the vibrator is fixed to the rotary shaft under the relatively non-rotatable condition.
Incidentally, an adhesive may be applied or impregnated into a gap between the output portion of the rotary shaft and the engaging hole of the vibrator whereby the vibrator is fixed to the rotary shaft.
In another embodiment, the tip end portion of the output portion is projected to the outside from the engaging hole of the vibrator, and an adhesive is applied to the tip end portion whereby the adhesive fixed to the tip end portion is retained at the projecting portion of the vibrator so that the vibrator is fixed to the rotary shaft so as not to move in the thrust direction.
Preferably, the vibrator is formed out of metal material selected from tungsten alloy, gold alloy and platinum alloy through a sintering method.
Incidentally, the tungsten alloy is selected from a Wxe2x80x94Nixe2x80x94Fe system, a Wxe2x80x94Nixe2x80x94Cu system and a Wxe2x80x94Moxe2x80x94Nixe2x80x94Fe system.
In one embodiment, in the case in which the vibrator is formed through an injection molding, after fine powder of the metal material and binder are kneaded and pelletized, the mixture is formed by the injection molding and then the unnecessary binder is removed by sintering so that the vibrator is formed with high precision.
Preferably, a material of the rotary shaft is one selected from the group consisting of iron, copper and metal alloy thereof.
Also, it is preferable that a material of the rotary shaft is one selected from the group consisting of stainless steels and high carbon steel wire rods.
Preferably, the miniature electric motor is used in one selected from the group consisting of a mobile phone, a pager and a massager.
According to the present invention, as described above, the vibrator may be positively fixed to the rotary shaft with a large retaining force under a relatively non-rotatable condition so as not to be moved in the thrust direction.